Chain Transfer Agents (CTA) are used during high pressure polymerisation of ethylene to low density polyethylene (LDPE) to control the molecular weight and thus indirectly melt flow rate (MFR) of the formed polymer. The mechanism is based on hydrogen atoms that are easy to abstract. Typical CTA are methylethylketone, propionaldehyde, propylene etc.
A CTAs is a group of agents including polar or non-polar CTAs according to their chemical nature. Propylene (C3) is an example of a non-polar CTA. This is assumed to provide good electrical properties due to its non-polar structure, especially when it comes to dielectric losses. Another benefit when using propylene as CTA is that vinyl groups are introduced into the polyethylene chain giving improved peroxide crosslinking properties.
Another type is the polar CTA, such as propionaldehyde (PA). Due to its polar structure it is assumed not to be beneficial to use this CTA in applications where low losses are a requirement.
Significance of
Significance of Tan δ (Dielectric Losses):
The tan δ and thus the dielectric losses (which are linearly proportional to the tan 6) shall be as low as possible for both technical and economical reasons:                Low losses means that low amount of transmitted electric energy is lost as thermal energy inside the cable insulation. These losses will mean economic losses for the power line operator.        Low losses will reduce the risk for thermal runaway, i.e. an unstable situation where the temperature of the insulation will increase due to the tan δ. When the temperature is increased, normally the tan δ will also increase. This will further increase the dielectric losses, and thus the temperature. The results will be a dielectric failure of the cable that needs to be replaced.Significance of dc Conductivity:        
The electric conductivity will control the leakage current through the insulation. This current will lead to tan δ, that is electric energy transformed into heat inside the insulation leading to negative economical consequences for the power line operator. The electric conductivity shall therefore be as low was possible.
Significance of Space Charge:
Space charges inside the insulation will distort the electric field and may lead to points of very high electric stress, that if it is high enough a dielectric failure will follow.
Preferably there should be no space charges present as it will make it possible to easily design the cable as the electric field distribution in the insulation will be known.
Normally space charges are located close to the electrodes; charges of the same polarity as the nearby electrode are called homocharges, charges of opposite polarity are called heterocharges. The heterocharges will increase the electric field at this electrode, homocharges will instead reduce the electric field. Thus, if voltage polarities will not take place in the power system, as in case of voltage source converters systems, homocharges will be less dangerous than heterocharges.
There is a continuous need in the polymer field to find polymers which are suitable for demanding polymer applications such as wire and cable applications with high requirements and stringent regulations.